In an ultrasonic bonding of coated electric wires, the coated electric wires are subjected to ultrasonic vibration and pressurizing force at the same time, thereby bonding the wires to each other. The ultrasonic bonding is a technique for connecting electric wires to each other as disclosed in Japanese Patent Application Laid-open No. H9-29445.
In this technique, upper and lower portions of intersected portions of the electric wires to be connected to each other are sandwiched between a horn-side chip and an anvil-side chip. In this state, ultrasonic vibration is applied to the horn-side chip, thereby bonding the electric wires to each other at the intersected portions.
In the conventional bonding operation of electric wires using the ultrasonic vibration, however, when the electric wires are coated electric wires, after insulators are melted and removed, conductors in the insulators must be bonded to each other. When the coated electric wires are to be bonded to each other, vibration condition of the ultrasonic vibration to be applied to the horn-side chip is determined by pressurizing force, frequency, amplitude and the like, but vibration condition is different when the insulators are melted and when the conductors are bonded to each other.
Therefore, the setting of conditions satisfying both the vibration conditions is complicated, and the condition setting is easily be varied depending upon positional deviation of conductors or setting deviation at the time of pressurization. Thus, the bonding operation of electric wires largely depends on guesswork or an operator, and it is difficult to obtain uniform connection state.